The present invention relates to roller burnishing tools for smoothing the interior surface of a cylindrical hole.
Roller burnishing tools utilize a plurality of circumferentially spaced rollers in a roller cage to roller burnish the interior of a pre-formed cylindrical hole so that it has a smooth finish. Tools of this type are available in which the rollers are located on a race which is inclined radially outwardly toward the rear, and a manually adjustable stop is provided which restricts the rearward movement of the rollers up the inclined race. Tools utilizing roller burnishers of this type are illustrated in a brochure of the Hegenscheidt Corporation, having a U.S. office at 1070 Livernois Ave., Troy, Mich. 48084 entitled The Combined Skiving and Roller Finishing Tools, Type RDS RETRAC, and U.S. Pat. Nos. 3,795,957 and 4,133,089.
When roller burnishing tools of the type described above are inserted in a cylinder, the forward thrust of the tool causes the rollers to move upwardly along the inclined race until the race contacts the preset stop. Accordingly, for all practical purposes, the rollers have a preset radius depending on the position of the stop.
If the diameter of the interior of a cylinder is very close to its nominal diameter, the roller burnishing operation will typically proceed quite smoothly. However, if the diameter of the cut cylinder is slightly oversized, the interior surfaces of the cylinder may not be sufficiently burnished. If the diameter is somewhat smaller than nominal, caused by cutting tool wear or other variables, the effective fixed diameter of the rollers will cause excessive working of the interior surfaces of the cylinder, requiring large forces to drive the tool through the cylinder, and often resulting in jamming of the tool inside the cylinder. If jamming does occur, the tool often cannot be retrieved intact, resulting in destruction of an extremely expensive working tool.
The roller burnishing tool, which is often found in combination with a skiving tool, is typically inserted into the cylinder through a drawtube to align it with the interior of the cylinder. The drawtube has the same or nearly the same diameter as the cylinder, and the roller burnishing tool as described above will roller burnish the drawtube on each cycle. Eventually, the drawtube becomes oversized, and the diameter of the drawtube does not accurately match that of the cylinder. When the roller cage reaches the preset stop further outward movement of the roller is prevented, and the drawtube will not accurately align the tool with the cylinder.
The roller burnishing tools described above typically have nylon pads to stabilize the roller burnishing action of the tool. These nylon pads tend to wear with use, and when worn, often cause chattering of the tool, which ruins the cylinder finish. In addition, if the nylon pads are worn, the rollers may contact the interior surface of the cylinder when the tool is withdrawn and score the interior surface so that it is unusable.